[Effects of RhoA on the adherens junction of murine ameloblasts].

OBJECTIVE

To investigate the regulation mechanism of RhoA signaling pathway during the enamel formation by using the EGFP-RhoADominant Negative (EGFP-RhoADN) transgenic mice model, from the aspect of adherens junctions, and to provide a theory basis for mechanism of enamel development defects.

METHODS

The enamel thickness of mandibular first molars of EGFP-RhoADN transgenic mice and wild type (WT) mice were observed by scanning electronic microscopy at 20 kV, and the enamel thickness of the distal face of the central cusp was measured at 10 locations via analysis by ImageJ (Rasband, 1997-2009). The enamel organs from mandibular first molars from postnatal-4-day (P4) EGFP-RhoADN mice and wild type mice were isolated, and the total RNA and protein were extracted from the epithelium of the enamel organs. The expression level of the adherens junctions components in ameloblasts layer of the postnatal-4-day EGFP-RhoADN transgenic mice and wild type mice mandibular first molars were detected by real-time PCR and Western blot assay.

RESULTS

The EGFP-RhoADN transgenic mice had decreased enamel thickness in their bilateral mandibular first molars versus those of control group (n=20), and enamel thickness was (84.60±0.20) μm vs. (106.24±0.24) μm, P<0.05. The protein expressions of E-cadherin, α-E-catenin and pan-cadherin in ameloblasts layer of postnatal-4-day EGFP-RhoADN transgenic mice molars were down-regulated, and the protein level of β-catenin in ameloblasts layer of P4 EGFP-RhoADN transgenic mice molars was up-regulated. The mRNA level of E-cadherin in ameloblasts layer of P4 EGFP-RhoADN transgenic mice molars was down-regulated versus that of WT mice, and the gene expression of E-cadherin was 0.93±0.01 vs. 1.00±0.02, P<0.05. The mRNA level of β-catenin in ameloblasts layer of P4 EGFP-RhoADN transgenic mice molars was up-regulated versus that of WT mice, and the gene expression of β-catenin was 1.23±0.03 vs. 1.00±0.05, P<0.05.

CONCLUSION

In the mandibular first molars of EGFP-RhoADN transgenic mice, the enamel formation was disrupted and the adherens junctions of EGFP-RhoADN transgenic mice ameloblasts were implicated during amelogenesis. RhoA signaling pathway may play a critical role in enamel development by altering the adherens junctions in ameloblasts.